This invention relates to reusable analyte sensor sites for use with replaceable, long term implantable anlayte sensors, in particular embodiments, to reusable glucose sensor sites for use with replaceable, long term glucose sensors.
Over the years, bodily characteristics have been determined by obtaining a sample of bodily fluid. For example, diabetics often test for blood glucose levels with a blood glucose meter. Traditional blood glucose determinations have utilized a painfull finger prick using a lancet to withdraw a small blood sample that is used by the blood glucose meter. This results in discomfort from the lancet as it contacts nerves in the subcutaneous tissue. The pain of lancing and the cumulative discomfort from multiple needle pricks is a strong reason why patients fail to comply with a medical testing regimen used to determine a change in characteristic over a period of time. In addition, these blood glucose meters are only designed to provide data at discrete points and do not provide continuous data to show the variations in the characteristic between testing times.
A variety of subcutaneous electrochemical sensors for use with monitors have been developed for detecting and/or quantifying specific agents or compositions in a patient""s blood. For instance, glucose sensors have been developed for use in obtaining an indication of blood glucose levels in a diabetic patient. Such readings are useful in monitoring and/or adjusting a treatment regimen which typically includes the regular administration of insulin to the patient. Thus, blood glucose readings from the monitor improve medical therapies with semi-automated medication infusion pumps of the external type, as generally described in U.S. Pat. Nos. 4,562,751; 4,678,408; and 4,685,903, which are herein incorporated by reference. Typical thin film sensors are described in commonly assigned U.S. Pat. Nos. 5,390,671; 5,391,250; 5,482,473; and 5,586,553 which are incorporated by reference herein. However, the thin film subcutaneous glucose sensors must be changed every few days to prevent infection. Also, due to the small size of these sensors to minimize pain on insertion under the skin, the enzyme wear out relatively quickly and require regular replacement. In addition, the user must carry around external hardware connected or linked to the sensor. Thus, although subcutaneous sensors provide an improvement over conventional test strips, they still require frequent changes.
Long term implanted glucose sensors have been proposed that can stay in the body for long periods of time, such as weeks and months. These long term implanted glucose sensors are particularly well adapted for use with automated implantable medication infusion pumps, as generally described in U.S. Pat. No. 4,573,994, which is herein incorporated by reference. The long term glucose sensor would obviate the need for frequent replacement of sensors and the need to carry around a large amount of external equipment. However, the insertion and placement of long term sensors is more invasive to the body then other sensor technologies and it often causes trauma during the insertion of the long term sensor into the body. After insertion, the long term sensor would not be usable for a period of time until the body heals and vascularizes the implanted long term sensor. Thus, each time a long term sensor is replaced the body must re-vascularize the replaced sensor. Another drawback to long term sensors is the development of scar tissue that encapsulates the implanted sensor and inhibits the proper operation of the long term sensor. Therefore, materials must be carefully selected to promote vasularization and not encapsulation. This requires careful construction of the outer covering for the long term sensor, which increases costs and may further delay the period of time before a newly implanted sensor may be used.
It is an object of an embodiment of the present invention to provide an improved reusable analyte sensor site, which obviates for practical purposes, the above mentioned limitations.
According to an embodiment of the invention, a reusable analyte sensor site for use with a replaceable analyte sensor for determining a level of an analyte includes a site housing. Preferably, the site housing material is formed to have an interior cavity with an opening and a conduit that is connected to the opening of the interior cavity to provide access to the interior cavity. The site housing material is selected to promote tissue ingrowth and vasuclarization, and yet be free of tissue ingress. Also, the site housing material permits the analyte to pass through the site housing material to the interior cavity to permit measurement by the replaceable analyte sensor. In addition, the conduit has a predetermined length to inhibit trauma and encapsulation of tissue occurring at the conduit, which is associated with placing the replaceable analyte sensor in the interior cavity of the site housing, from interfering with the tissue ingrowth and vascularization surrounding the interior cavity of the site housing material.
In particular embodiments, the conduit has a length of at least 5 millimeters, and the site housing material has a porosity in a range from 2 to 25 microns. Preferably, the site housing is for implantation into sub-dermal tissue and/or inter-peritoneal tissue. Also, the site housing material is selected from a group of materials consisting essentially of Teflon and Dacron. In addition, the site housing is chosen so that it will last for a period of time such that it can be used with two or more consecutive replaceable analyte sensors.
Preferred embodiments utilize a site housing material that passes glucose, and the replaceable analyte sensor is a glucose sensor. In other embodiments, the invention is embodied in a system that uses a replaceable analyte sensor with the reusable analyte sensor site. In alternative embodiments, the reusable analyte sensor site may be used with a replaceable infusion catheter for infusion a fluid into the body of a user.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments of the invention.